Since the discovery of high-temperature superconductors, development in high-temperature superconducting wire is carried out actively in view of the application to power apparatus such as a cable, magnet, current-limiting device, and the like. The high-temperature superconducting wire is roughly classified into two types, i.e. a bismuth type silver sheath wire and a RE123 type thin film wire (RE=rare earth element).
The RE123 type thin film superconducting wire has raised hopes for a high-temperature superconducting wire of the next generation based on the advantages of: (1) the critical current density at the liquid nitrogen temperature (77.3K) exhibits the performance of approximately 106 A/cm2 that is two orders of magnitude greater as compared with the bismuth type silver sheath wire; and (2) the critical current density under magnetic field is high.
As a general structure of a thin film superconducting wire, a thin intermediate layer of ceramic is formed on a metal substrate, and a superconducting layer is formed thereon. In order to draw out superior superconducting properties for a thin film superconducting wire, the crystal orientation of the superconducting layer must be arranged in three dimensions. To this end, a thin film having high orientation must be produced for the aforementioned thin film intermediate layer.
Japanese Patent Laying-Open No. 2005-1935 (Patent Literature 1) discloses a method including the steps of removing an oxide layer located on the surface of an oriented metal substrate, and epitaxial growth of a thin film such as an intermediate layer and a superconducting layer while maintaining the biaxial orientation of the oriented metal substrate.